Charged particle beam apparatus

ABSTRACT

Provided is a charged particle beam apparatus or charged particle microscope capable of observing an observation target sample in an air atmosphere or a gas environment without making significant changes to the configuration of a conventional high vacuum charged particle microscope. In a charged particle beam apparatus configured such that a thin film ( 10 ) is used to separate a vacuum environment and an air atmosphere (or a gas environment), an attachment ( 121 ) capable of holding the thin film ( 10 ) and whose interior can be maintained at an air atmosphere or a gas environment is inserted into a vacuum chamber ( 7 ) of a high vacuum charged particle microscope. The attachment ( 121 ) is vacuum-sealed and fixed to a vacuum partition of the vacuum sample chamber. Image quality is further improved by replacing the atmosphere in the attachment with helium or a light-elemental gas that has a lower mass than atmospheric gases such as nitrogen or water vapor.

TECHNICAL FIELD

The present invention relates to a microscope technology with which anobservation target sample can be observed at atmospheric pressure or ina predetermined gas environment, in particular, a tabletop chargedparticle microscope.

BACKGROUND ART

For observing a minute area of an object, a scanning electron microscope(SEM), a transmission electron microscope (TEM), and the like are used.When such apparatuses are used, a sample is typically imaged after asecond housing for housing the sample is evacuated to a vacuum and thesample atmosphere is set to a vacuum state. Meanwhile, there has been anincreasing need for observing a sample that may become damaged or changestate due to a vacuum, such as a biochemical sample or a liquid sample,using an electron microscope. Thus, in recent years, SEM apparatuses,sample holding apparatuses, and the like that can observe observationtarget samples under atmospheric pressure have been developed.

Such apparatuses are adapted to have a vacuum state and an atmosphericstate that are separated by providing a thin film or a minutethrough-hole between electron optics and a sample, in principle, andthus are common in that a thin film is provided between the sample andthe electron optics.

For example, Patent Literature 1 discloses an atmospheric-pressure SEMin which an electron source side of an electron optical column isarranged such that it faces downward, and an objective lens side isarranged such that it faces upward, and further, a thin film that allowsan electron beam to pass therethrough is provided on an electron beamemission hole at an end of the electron optical column, with an O-ringinterposed therebetween. In the invention described in Patent Literature1, SEM observation is conducted in such a manner that an observationtarget sample is mounted directly on the thin film, and the sample isirradiated with a primary electron beam from the side of the bottom faceof the sample, and then, reflected electrons or secondary electrons aredetected. The sample is held in a space that is formed by the thin filmand an annular member disposed around the thin film. Further, the spaceis filled with a liquid such as water. The invention disclosed in PatentLiterature 1 implements an atmospheric-pressure SEM that is suitable forobserving a biological sample, in particular.

Patent Literature 2 discloses an invention of an environmental cell inwhich an observation target sample is stored in a plate-like cylindricalcontainer, on the upper face of which is provided an aperture forallowing an electron beam to pass therethrough, and the cylindricalcontainer is provided in a vacuum sample chamber of a SEM, and further,a hose is connected to the cylindrical container from outside of thevacuum sample chamber, whereby the interior of the container can bemaintained at an air atmosphere in a pseudo manner. The term “pseudo”herein means that as a gas flows out of the aperture when the vacuumsample chamber is evacuated to a vacuum, observation is not conductedunder an atmospheric-pressure environment in the strict sense.

CITATION LIST Patent Literature

-   Patent Literature 1: JP 2009-158222 A (USP 2009/0166536 A)-   Patent Literature 2: JP 2009-245944 A (USP 2009/0242763 A)

SUMMARY OF INVENTION Technical Problem

The conventional charged particle microscope or charged particle beamapparatus having a function of conducting observation in a gasenvironment is an apparatus that is specifically produced for conductingobservation under a gas environment, and there have been no apparatusesthat can easily conduct observation under an atmospheric-pressure/gasenvironment using an ordinary high vacuum charged particle microscope.

For example, the atmospheric-pressure SEM described in Patent Literature1 is a structurally very special device, and cannot execute SEMobservation in an ordinary high vacuum environment. In addition, as atarget to be observed is held within a thin film that is filled with aliquid, the sample may become wet if observation at atmospheric pressureis executed once. Thus, it would be very difficult to observe a samplein the same state in each of the air environment and the high vacuumenvironment. Further, as the thin film is always in contact with theliquid, there is a problem in that the thin film may become damaged withquite a high possibility.

The environmental cell described in Patent Literature 2 can conductobservation in an atmospheric-pressure/gas environment. However, thereis a problem in that as it is only possible to conduct observation of asample with a size that can be inserted into the cell, it would beimpossible to conduct observation of a large sample at atmosphericpressure/gas environment. In addition, when such an environmental cellis used, in order to observe a different sample, it would be necessaryto take the environmental cell out of the vacuum sample chamber of theSEM to replace the sample, and carry the environmental cell into thevacuum sample chamber again, which is problematic in that thereplacement of the sample is complex.

The present invention has been made in view of the foregoing problems,and it is an object of the present invention to provide a chargedparticle beam apparatus or charged particle microscope with which anobservation target sample can be observed in an atmospheric environmentor a gas environment without significantly changing the configuration ofthe conventional high vacuum charged particle microscope.

Solution to Problem

The present invention solves the aforementioned problems by fixing to avacuum chamber of a charged particle microscope an attachment, which canhave the sample stored therein with pressure in the attachment beingmaintained higher than pressure in the vacuum chamber, by inserting theattachment into the vacuum chamber through an opening of the vacuumchamber. The opening of the vacuum chamber is provided in, for example,a side face or a bottom face of the vacuum chamber. In addition, theattachment has a function of holding a thin film that allows a primarycharged particle beam to penetrate or pass through the interior of theattachment, thereby ensuring a pressure difference between the interiorof the vacuum chamber and that of the attachment. The vacuum chamber mayalso be referred to as a first housing, while the attachment may also bereferred to as a second housing for the vacuum chamber.

Advantageous Effects of Invention

While the vacuum chamber is maintained at a high degree of vacuum by thethin film, the interior of the attachment is maintained at atmosphericpressure/gas environment. In addition, an observation target sample canbe carried into or out of the attachment. That is, the present inventioncan implement a charged particle microscope that can more easily conductobservation at atmospheric pressure/gas environment than isconventionally done.

The size of the attachment of the present invention can be easilyincreased as it adopts a method of insertion from a side face of thesample chamber. Thus, it is possible to observe even a large sample thatwould not be able to be encapsulated in the environmental cell.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an overall configuration view of a charged particle microscopein Embodiment 1;

FIG. 2 is an overall configuration view of a charged particle microscopein Embodiment 2;

FIG. 3 is a view showing the charged particle microscope in Embodiment 2in a state in which a plate member is pulled out;

FIG. 4 is a view showing the charged particle microscope in Embodiment 2in a state in which the microscope is used as a high vacuum SEM;

FIG. 5 is an operation illustration view of the charged particlemicroscope in Embodiment 2;

FIG. 6 shows an exemplary configuration of the charged particlemicroscope in Embodiment 2;

FIG. 7 shows an exemplary configuration of the charged particlemicroscope in Embodiment 2;

FIG. 8 shows an exemplary configuration of the charged particlemicroscope in Embodiment 2;

FIG. 9 is an overall configuration view of a charged particle microscopein Embodiment 3;

FIG. 10 is an overall configuration view of a charged particlemicroscope in Embodiment 4; and

FIG. 11 is an overall configuration view of a charged particlemicroscope in Embodiment 5.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments will be described with reference to thedrawings.

Embodiment 1

This embodiment will describe the most basic embodiment. FIG. 1 is anoverall configuration view of a charged particle microscope in thisembodiment. The charged particle microscope shown in FIG. 1 mainlyincludes a charged particle optical column 2, a first housing (i.e., avacuum chamber) 7 that supports the charged particle optical column withrespect to an apparatus installation plane, a second housing (i.e., anattachment) 121 that is used through insertion into the first housing 7,and a controller therefor. When the charged particle microscope is used,the interior of the charged particle optical column 2 and the firsthousing are evacuated to a vacuum by a vacuum pump 4. Actuation and stopoperation of the vacuum pump 4 are also controlled by the controller.Although FIG. 1 shows a single vacuum pump 4, two or more vacuum pumps 4may be provided.

The charged particle optical column 2 includes elements such as acharged particle source 0 that generates a charged particle beam, andoptical lenses 1 that converge and guide the generated charged particlebeam toward the bottom of the column to thereby cause it to scan asample 6, as a primary charged particle beam. The charged particleoptical column 2 is disposed such that it protrudes toward the interiorof the first housing 7, and is fixed to the first housing 7 with avacuum sealing member 123 interposed therebetween. A detector 3, whichdetects secondary charged particles (i.e., secondary electrons orreflected electrons) obtained upon irradiation with the primary chargedparticle beam, is disposed at an end of the charged particle opticalcolumn 2. In the exemplary configuration shown in FIG. 1, the detector 3is provided in the first housing 7, but it may be disposed in thecharged particle optical column 2 or in the second housing 121.

The charged particle microscope in this embodiment includes, as thecontroller, a personal computer 35 that a user of the apparatus uses, anupper-level controller 36 that is connected to and communicates with thepersonal computer 35, and a lower-level controller 37 that controls avacuum evacuation unit, a charged particle optical unit, and the like inresponse to instructions transmitted from the upper-level controller 36.The personal computer 35 includes a monitor that displays an operationscreen (GUI) of the apparatus, and an input means for the operationscreen, such as a keyboard and a mouse. The upper-level controller 36and the lower-level controller 37 are connected with a communicationline 43, while the upper-level controller 36 and the personal computer35 are connected with a communication line 44.

The lower-level controller 37 is a portion that transmits and receivescontrol signals for controlling the vacuum pumps 4, a gas control valve101, the charged particle source 0, the optical lenses 1, and the like,and further converts an output signal of the detector 3 into a digitalimage signal for transmission to the upper-level controller 36. Althoughthe output signal of the detector 3 is connected to the lower-levelcontroller 37 in FIG. 1, an amplifier such as a pre-amplifier may alsobe interposed therebetween.

The upper-level controller 36 and the lower-level controller 37 mayinclude a mixture of analog circuits and digital circuits. In addition,the upper-level controller 36 and the lower-level controller 37 may be asingle, integrated unit. Further, the configuration of the controllershown in FIG. 1 is only exemplary, and variations of the control units,the valve, the vacuum pump, the wires for communication, and the likeall fall into the category of the SEM or the charged particle beamapparatus of this embodiment as far as the functions intended by thisembodiment are satisfied.

A vacuum pipe 16 connected at one end to the vacuum pump 4 is connectedto the first housing 7. Thus, the interior of the first housing 7 can bemaintained in a vacuum state. At the same time, the first housing 7 hasa leak valve 14 for exposing the interior of the housing to theatmosphere, and thus can expose the interior of the first housing 7 tothe atmosphere in maintenance. The leak valve 14 may be either providedor not, and two or more leak valves 14 may also be provided. Further,the arrangement position of the leak valve 14 on the first housing 7 isnot limited to the position shown in FIG. 1, and the leak valve 14 maybe provided at another position on the first housing 7. Further, thefirst housing 7 has an opening at a side face thereof, and the secondhousing 121 is inserted thereinto through the opening.

The second housing 121 includes a main body portion 131, which is cuboidin shape, and a mating portion 132. The main body portion 131 has afunction of storing the sample 6, which is a target to be observed, andis inserted into the first housing 7 through the opening. The matingportion 132 forms a mating face with an outer wall face of the firsthousing 7 on the side face side having the opening, and is fixed to theouter wall face on the side face side, with a vacuum sealing member 126interposed therebetween. Accordingly, the second housing 121 is entirelyfitted into the first housing 7. The opening can be most simply producedby using an opening that the vacuum sample chamber of the chargedparticle microscope originally has for carrying in or out the sample.That is, if the second housing 121 is produced in keeping with the sizeof the hole that is originally provided, and the vacuum sealing member126 is attached to an area around the hole, alterations that should bemade to the apparatus can be suppressed to the minimum.

The main body portion 131 has on the upper face side thereof a thin film10 at a position where the thin film 10 is located immediately below thecharged particle optical column 2 when the second housing 121 isentirely fitted into the first housing 7. Such a thin film 10 allows aprimary charged particle beam emitted from the bottom end of the chargedparticle optical column 2 to penetrate or pass therethrough, so that theprimary charged particle beam finally reaches the sample 6 through thethin film 10.

When the charged particle beam is an electron beam, the thin film 10should have about a thickness that allows the electron beam to penetratetherethrough, typically, about 20 μm or less. Instead of the thin film,it is also possible to use an aperture member with a through-hole thatallows a primary charged particle beam to pass therethrough. The holediameter in that case is desirably less than or equal to an area ofabout 1 mm² from a request that differential pumping be able to beconducted using realistic vacuum pumps. When the charged particle beamis an ion beam, it is difficult for the ion beam to pass through thethin film without damaging the thin film. Thus, an aperture with an areathat is less than or equal to about 1 mm² is used. A chain line in FIG.1 indicates the optical axis of a primary charged particle beam. Thecharged particle optical column 2, the first housing 7, and the thinfilm 10 are arranged along the same axis as the optical axis of theprimary charged particle beam. The distance between the sample 6 and thethin film 10 is adjusted by providing a sample table 17 with anappropriate height.

As shown in FIG. 1, a side face of the second housing 121 is an openface, and the sample 6 that is stored in the second housing 121 (i.e.,on the right side of the dotted line in FIG. 1; hereinafter, a secondspace) is placed in an atmospheric pressure state during observation.Meanwhile, as the vacuum pump 4 is connected to the first housing 7, aclosed space, which is formed by the inner wall face of the firsthousing 7, the outer wall face of the second housing, and the thin film10 (hereinafter, a first space), can be evacuated to a vacuum.Accordingly, in this embodiment, while the apparatus is in operation,the charged particle optical column 2 and the detector 3 can bemaintained in a vacuum state, while the sample 6 can be maintained atatmospheric pressure. In addition, as the second housing 121 has an openface, the sample 6 can be freely replaced during observation.

As described above, this embodiment can implement a charged particlemicroscope with which even a relatively large sample can be observed atatmospheric pressure.

Embodiment 2

This embodiment will describe an example of the application to atabletop scanning electron microscope. Although an example of theapplication to a scanning electron microscope will be described, it isneedless to mention that this embodiment can also be applied to atypical charged particle microscope such as an ion microscope.

FIG. 2 shows an overall configuration view of a scanning electronmicroscope in this embodiment. As in Embodiment 1, the scanning electronmicroscope in this embodiment also includes an electron optical column2, a first housing (i.e., a vacuum chamber) 7 that supports the electronoptical column with respect to an apparatus installation plane, a secondhousing (i.e., an attachment) 121 that is used through insertion intothe first housing 7, a controller therefor, and the like. The operationand function of each element, or additional elements that are added toeach element are substantially the same as those in Embodiment 1. Thus,detailed description thereof will be omitted.

By the way, the thin film 10 of the scanning electron microscope in thisembodiment is, unlike in Embodiment 1, removably fixed to the upper faceof the main body portion 131 of the second housing with a thin filmholding member 47 interposed therebetween. Although the thin film 10 isfixed to the thin film holding member 47 in a vacuum-sealing manner, itis also possible to use a vacuum sealing member such as an O-ring, oruse an organic material such as adhesive, or a tape.

The thin film holding member 47 is removably fixed to the bottom faceside of the ceiling board of the second housing 121 with a vacuumsealing member interposed therebetween. The thin film 10 is quite thin,as thin as about 20 μm from a request that the thin film 10 should allowan electron beam to penetrate therethrough. Thus, there is a possibilitythat the thin film 10 may deteriorate with time or be damaged while itis prepared for observation. Meanwhile, the thin film 10, which is thin,is quite difficult to handle directly. Thus, if the thin film 10 is ableto be handled not directly but via the thin film holding member 47 as inthis embodiment, handling (in particular, replacement) of the thin film10 becomes quite easy. That is, if the thin film 10 is damaged, thewhole thin film holding member 47 may be replaced. Even if it isnecessary to directly replace the thin film 10, it is possible to takethe thin film holding member 47 out of the apparatus and replace thethin film 10 outside the device. It is also possible to, as inEmbodiment 1, use an aperture member with a hole with an area that isless than or equal to about 1 mm² instead of the thin film.

Further, the thin film holding member 47 in this embodiment has, on theside that is opposite the sample 6, a restriction member 105 that avoidscontact between the thin film and the sample. For the restriction member105, anything that can restrict the distance between the sample and thethin film may be used. Most simply, an adhesive or a tape may beattached for use as the restriction member 105. However, when the meanfree path of a primary electron beam that has passed through the thinfilm 10 is considered, the restriction member 105 is preferably producedusing a thin film material whose thickness is precisely known. Althoughthe restriction member 105 is attached to the thin film holding member47 in FIG. 2, it may also be attached to the thin film 10 or a samplestage 5, or be mounted on the sample 6. Further, the restriction member105 may be provided in a removable fashion.

In the case of the scanning electron microscope in this embodiment, theopen face of the second housing 121 is configured to be able to becovered with a covering member 122. Thus, various functions can berealized. Hereinafter, such functions will be described.

The scanning electron microscope in this embodiment has a function ofsupplying a replacement gas into the second housing. An electron beamemitted from the bottom end of the electron optical column 2 passesthrough the first space that is maintained at a high degree of vacuum,and passes through the thin film 10 (or an aperture member) shown inFIG. 2, and further enters the second space that is maintained atatmospheric pressure or a lower degree of vacuum (than is the firstspace). However, as an electron beam will be scattered by gas moleculesin the space where the degree of vacuum is low, the mean free path willbe shorter correspondingly. That is, when the distance between the thinfilm 10 and the sample 6 is long, it would be impossible for an electronbeam or secondary electrons or reflected electrons, which are generatedby the electron beam irradiation, to reach the sample. Meanwhile, theprobability of the scattering of an electron beam is proportional to themass number of gas molecules. Thus, if the atmosphere in the secondspace is replaced with gas molecules whose mass number is lower thanthat of the atmosphere, the probability of the scattering of theelectron beam will decrease, which will allow the electron beam to reachthe sample. As the type of the replacement gas, if a gas that is lighterthan the atmosphere, such as nitrogen or water vapor is used, the effectof improvement in the image S/N is seen, while when a helium gas or ahydrogen gas whose mass number is lower is used, the effect ofimprovement in the image S/N becomes higher.

From the foregoing reasons, in the scanning electron microscope in thisembodiment, the covering member 122 is provided with an attachmentportion (i.e., a gas introducing portion) of a gas supply pipe 100. Thegas supply pipe 100 is connected to a gas cylinder 103 with a connectingportion 102. Accordingly, a replacement gas is introduced into thesecond space 12. A gas control valve 101 is disposed in the gas supplypipe 100, so that the flow rate of a replacement gas that flows throughthe pipe can be controlled. Therefore, a signal line extends from thegas control valve 101 to the lower-level controller 37, so that a userof the apparatus is able to control the flow rate of the replacement gason the operation screen that is displayed on the monitor of the personalcomputer 35.

The replacement gas, which is a light-element gas, will easilyaccumulate in the upper portion of the second space 12, and thus, gas inthe lower side of the second space 12 is difficult to replace. Thus, anopening is provided in the covering member 122 at a position (i.e., atthe attachment position of the pressure control valve 104 in FIG. 2)lower than the attachment position of the gas supply pipe 100.Accordingly, as the atmospheric gas is pushed away by the light-elementgas introduced from the gas introducing portion and is evacuated fromthe opening on the lower side, the atmosphere in the second housing 121can be efficiently replaced. It should be noted that such an opening maycombine the function of a rough evacuation port described below.

The second housing 121 or the covering member 122 may be provided with avacuum evacuation port so that the second housing 121 is evacuated to avacuum once before a replacement gas is introduced into the secondhousing 121. The vacuum evacuation in this case has only to be performedby reducing the atmospheric gas components remaining in the secondhousing 121 to less than or equal to a given amount. Thus, high vacuumevacuation need not be performed, and rough evacuation would be enough.However, in the case that a sample containing moisture, such as abiological sample, is observed, if the sample is placed in a vacuumstate once, the moisture will evaporate and the sample will changestate. Thus, as described above, a method of directly introducing areplacement gas from the air atmosphere is preferable. After thereplacement gas is introduced, the aforementioned opening is closed witha covering member, whereby the replacement gas can be effectivelyconfined in the second space 12.

If a three-way valve is attached at a position of the opening, such anopening can combine the functions of a rough evacuation port and an airleak evacuation port. That is, if one port of the three-way valve isattached to the covering member 122, another port is connected to arough evacuation vacuum pump, and a leak valve is attached to the otherport, an evacuation port that combines the aforementioned functions canbe realized.

It is also possible to provide a pressure control valve 104 instead ofthe aforementioned opening. The pressure control valve 104 has afunction of automatically opening the valve when the pressure in thesecond housing 121 becomes 1 atmospheric pressure or greater. If apressure control valve with such a function is provided, when the innerpressure becomes 1 atmospheric pressure or greater upon introduction ofa light-element gas, the valve automatically opens to discharge theatmospheric gas components such as nitrogen and oxygen to the outside ofthe apparatus, so that the interior of the apparatus can be filled withthe light-element gas. It should be noted that the gas cylinder 103shown in the drawing may be either provided in the scanning electronmicroscope in advance or be attached by the user of the apparatus later.

Next, a method of adjusting the position of the sample 6 will bedescribed. The scanning electron microscope in this embodiment has asample stage 5 as a means for moving the observation visual field. Thesample stage 5 has an XY driving mechanism for the plane direction and aZ-axis driving mechanism for the height direction. A support plate 107,which serves as a bottom plate for supporting the sample stage 5, isattached to the covering member 122, and the sample stage 5 is fixed tothe support plate 107. The support plate 107 is attached to a face,which faces the second housing 121, of the covering member 122 such thatit extends toward the interior of the second housing 121. The Z-axisdriving mechanism and the XY driving mechanism have support axes thatextend therefrom and connect to an operation knob 108 and an operationknob 109, respectively. The user of the apparatus adjusts the positionof the sample 6 in the second housing 121 by operating such operationknobs 108 and 109.

When the sample position is adjusted, the sample position in the planedirection is typically determined first, and then, the sample positionin the height direction is adjusted. However, in order to avoid damageto the thin film 10, the position of the sample 6 in the heightdirection should be adjusted so that it is not located too close to thethin film 10. Therefore, the scanning electron microscope in thisembodiment has an observation means such as a camera 106. Accordingly,it is possible to remotely observe the distance between the thin film 10and the sample 6 and a view in which the sample 6 is being moved in theheight direction. Instead of the camera 106, an optical microscope withhigh imaging resolution may also be used. Further, though not shown, thedistance between the sample and the thin film may be measured usingreflection of electromagnetic waves such as infrared rays. Theattachment position of the observation means is not particularly limitedto that shown in FIG. 2, and may be any position at which the distancebetween the sample and the thin film can be clearly measured.

Next, a replacement mechanism for the sample 6 will be described. Thescanning electron microscope in this embodiment has a plate-membersupport member 19 and a bottom plate 20 that are provided on the bottomface of the first housing 7 and at the bottom end of the covering member122. The covering member 122 is removably fixed to the second housing121 with a vacuum sealing member 125 interposed therebetween. Meanwhile,the plate-member support member 19 is also removably fixed to the bottomplate 20. As shown in FIG. 3, the covering member 122 and theplate-member support member 19 are able to be entirely removed from thesecond housing 121.

The bottom plate 20 has a supporting rod 18 that is used as a guide inremoval. In the ordinary state, the supporting rod 18 is stored in astorage unit that is provided in the bottom plate 20, and is configuredto extend in the extraction direction of the covering member 122 inremoval. At the same time, the supporting rod 18 is fixed to theplate-member support member 19, and is configured not to completelyseparate the covering member 122 from the main body of the scanningelectron microscope when the covering member 122 is removed from thesecond housing 121. Accordingly, it is possible to avoid dropping of thesample stage 5 or the sample 6.

When the sample is carried into the second housing 121, the Z-axisoperation knob of the sample stage 5 is first turned to move the sample6 away from the thin film 10. Next, the pressure control valve 104 isopened to expose the interior of the second housing to the atmosphere.After that, it is checked that the interior of the second housing is notin the reduced-pressure state or an extremely pressurized state, andthen the covering member 122 is pulled out to the opposite side of themain body of the apparatus. Accordingly, the sample 6 becomesreplaceable. After the sample is replaced, the covering member 122 ispushed into the second housing 121, and the covering member 122 is fixedto the mating portion 132 with a fastening member (not shown), and thena replacement gas is introduced. The aforementioned operations can beexecuted with the operation of the electron optical column 2 beingcontinued. Thus, the scanning electron microscope in this embodiment canpromptly start observation after the replacement of the sample.

The scanning electron microscope in this embodiment can also be used asan ordinary high vacuum SEM. FIG. 4 shows an overall configuration viewof the scanning electron microscope in this embodiment in a state inwhich the microscope is used as a high vacuum SEM. In FIG. 4, acontroller is omitted as it is similar to that shown in FIG. 2. FIG. 4shows a scanning electron microscope in a state in which the attachmentpositions of the gas supply pipe 100 and the pressure control valve 104are clogged with covering members 130 after the gas supply pipe 100 andthe pressure control valve 104 are removed from the covering member 122in a state in which the covering member 122 is fixed to the secondhousing 121. If the thin film holding member 47 is removed from thesecond housing 121 through an operation before or after theaforementioned operation, it becomes possible to connect the first space11 and the second space 12, and thus evacuate the interior of the secondhousing to a vacuum using the vacuum pump 4. Accordingly, high vacuumSEM observation can be conducted with the second housing 121 attached.

It should be noted that as a variation of the configuration in FIG. 4,it is also possible to remove the entire second housing 121 in a statein which the thin film holding member 47 is attached thereto, anddirectly fix the covering member 122 to the mating face of the firsthousing 7. With such a configuration, it is also possible to connect thefirst space 11 and the second space 12 and evacuate the interior of thesecond housing to a vacuum using the vacuum pump 4. This configurationis the same as the configuration of a typical SEM apparatus.

As described above, in this embodiment, all of the sample stage 5, itsoperation knobs 108 and 109, the gas supply pipe 100, and the pressurecontrol valve 104 are integrally attached to the covering member 122.Thus, the user of the apparatus is able to conduct operations on theoperation knobs 108 and 109, an operation of replacing a sample, or anoperation of attaching or detaching the gas supply pipe 100 and thepressure control valve 104 on a single face of the first housing.Accordingly, the operability is quite improved in comparison with ascanning electron microscope with a configuration in which theaforementioned components are separately attached to different faces.

FIG. 5 shows a flowchart showing an operation flow of the scanningelectron microscope in this embodiment.

In first step 70, the first space is evacuated to a vacuum. The firstspace may also be evacuated to a vacuum in advance. In second step 71,the sample 6 is mounted on a sample table on the sample stage 5, so asto be mounted on the sample stage 5. In third step 72, the coveringmember 122 is introduced into the second housing and is fastened to themain body of the apparatus (the second housing). In fourth step 73, thegas control valve 101 is opened for a given period of time and is thenclosed, so that a replacement gas such as a helium gas is introducedinto the second space. In fifth step 74, the operation conditions of theelectron optical column are adjusted to cause it to emit an electronbeam. In sixth step 75, image acquisition is started. In seventh step76, the covering member 122 is removed. The replacement gas confined inthe second space is released to the outside of the apparatus. Thecovering member 122 may also be removed after the pressure control valveis opened and the replacement gas is discharged. In eighth step 77, thesample is taken out. If another sample is to be observed, the flowreturns to second step 71.

It should be noted that the second space can not only be set to theatmospheric pressure state with a replacement gas being introducedthereinto, but also be set to a low vacuum state with a replacement gasbeing introduced thereinto in small quantities, or be set to a vacuumstate. In this case, the flow control of the replacement gas or vacuumevacuation may be performed in fourth step 73. The flow in FIG. 5 showsonly exemplary operations, and the order thereof may be changed asappropriate.

FIG. 6 shows an exemplary operation screen that is displayed on amonitor of the personal computer 35. The operation screen shown in FIG.6 includes, for example, an operation window 50, an image displayportion 51, an image observation start button 52 for starting electronbeam emission to start display of an image, an image observation stopbutton 53 for stopping electron beam emission to stop display of animage, a focus adjustment button 54 for executing autofocus by adjustingoptical lenses such as a deflection lens and an objective lens, abrightness adjustment button 55 for adjusting the brightness of theimage, a contrast adjustment button 56 for adjusting the contrast, avacuum evacuation button 57 for starting vacuum evacuation of theinterior of the charged particle optical column 2 and the first housing7, and an air leak button 58 for exposing the interior of the firsthousing 7 to the atmosphere. When the vacuum evacuation button 57 isclicked on the screen, vacuum evacuation starts, and when the button isclicked again, the vacuum evacuation stops. The operation of the airleak button 58 is similar. Processes that are executed through theaforementioned button operations can also be executed through manualoperations, i.e., by operating the mechanical buttons or knobs providedon the main body of the apparatus.

The operation window 50 displays a gas emission start button 112 foropening the gas control valve 101 to emit gas through a gas nozzle, agas emission stop button 113 for closing the gas control valve 101 tostop the gas emission, a SEM image display button 114 for displaying animage captured with the scanning electron microscope on the imagedisplay portion 51, and a camera button 115 for displaying an imageacquired with the camera 106. When a SEM/Camera display button 116 isclicked, both a SEM image and a camera image can be displayed on theimage display portion 51, which is particularly effective in adjustingthe height of the sample 6.

In this embodiment, after the gas emission start button 112 is clickedand the gas control valve 101 opens, if one fails to click the gasemission stop button 113, there is a possibility that gas in the gascylinder 103 may become insufficient. Therefore, as shown in FIG. 7, achild window 118 may be provided to display a gas emission time settingscreen 117 for setting the duration of the gas emission from when thegas emission starts till it stops. The time from when the gas emissionstarts till it stops may not be set by the user of the apparatus, but atime that is preset on the apparatus may also be used.

There may be cases where the user wants to conduct gas emission onlywhen observing a SEM image. In that case, another window 118 shown inFIG. 7 is displayed, and a check box 119 is checked in advance. When theimage observation start button 52 is clicked with the check box beingchecked, the gas control valve 101 automatically opens, and areplacement gas starts to be introduced. After that, when the time seton the gas emission time setting screen 117 has elapsed, the gas controlvalve 101 automatically closes. When the image observation stop button53 is clicked while the replacement gas is being introduced, the gascontrol valve 101 also closes automatically. It should be noted thatwhen the SEM image display button 114, the camera button 115, or theSEM/Camera display button 116 is clicked while the replacement gas isbeing introduced, the image displayed on the image display portion 51can be switched in accordance with the type of the selected image.Opening/closing control of the gas control valve 101 described above isexecuted by the lower-level controller 37 on the basis of the settinginformation in the personal computer 35 that the upper-level controllertransmits.

FIG. 8 shows an exemplary operation screen for when a rough evacuationport or a three-way valve is provided on the covering member 122 or onthe second housing 121. On the operation screen in this case, vacuumevacuation start/stop buttons for the first space and the second spaceare separately displayed. When a vacuum evacuation button 59 for thesecond space is clicked, a vacuum valve provided in the rough evacuationport opens, and vacuum evacuation of the second space starts. When thevacuum evacuation button 59 is clicked again, the vacuum valve in therough evacuation port closes, and the vacuum evacuation stops. Likewise,when an air leak button 60 for the second space is clicked, a leak valveprovided on the three-way valve opens, and the second space is exposedto the atmosphere. When the air leak button 60 is clicked again, theleak valve closes, and the exposure of the second space to theatmosphere stops.

In addition to the aforementioned configuration, it is also possible toprovide a contact monitor for monitoring the state of contact betweenthe second housing 121 and the covering member 122 to monitor if thesecond space is closed or open.

Further, in addition to the secondary electron detector and thereflected electron detector, it is also possible to provide an X-raydetector and a photodetector to conduct EDS analysis and fluorescenceline detection. The X-ray detector and the photodetector may be arrangedin either the first space 11 or the second space 12.

When the sample 6 is irradiated with an electron beam, an absorptioncurrent flows through the sample. Therefore, an ammeter may be providedto measure a current that flows through the sample 6 or the sampletable. Accordingly, an image of the absorption current (or an image thatuses the absorption current) can be acquired. Alternatively, atransmission electron detector may be arranged below the sample table toacquire a scanning transmission (STEM) image. The sample table may alsobe used as a detector.

Further, a high voltage may be applied to the sample stage 5. When ahigh voltage is applied to the sample 6, electrons emitted from thesample 6 can have high energy, which in turn can increase the amount ofsignals. Thus, image S/N improves.

Further, the configuration of this embodiment can also be applied to asmall electron beam lithography system. In that case, the detector 3 isnot necessarily required.

As described above, this embodiment can implement not only the effect ofEmbodiment 1, but also an atmospheric-pressure SEM that can also be usedas a high vacuum SEM. In addition, as observation can be executed with areplacement gas being introduced, the scanning electron microscope inthis embodiment can acquire an image with higher S/N than the chargedparticle microscope in Embodiment 1.

Although this embodiment has illustrated an exemplary configurationintended for a tabletop electron microscope, this embodiment can also beapplied to a large scanning electron microscope. In the case of atabletop electron microscope, the whole apparatus or the chargedparticle optical column is supported on the apparatus installation planeby a housing, while in the case of a large scanning electron microscope,the whole apparatus may be disposed on a mount. Thus, if the firsthousing 7 is disposed on a mount, the configuration described in thisembodiment can be applied as it is to a large scanning electronmicroscope.

Embodiment 3

This embodiment will describe an exemplary configuration in which thecovering member 122 is removed from the apparatus configuration of FIG.2. FIG. 9 shows the overall configuration of the charged particlemicroscope in this embodiment. The controller is similar to that inEmbodiment 2. Thus, illustration of the controller is omitted and only aprimary part of the apparatus is shown.

In the configuration shown in FIG. 9, the sample stage 5 is directlyfixed to the bottom face of the second housing 121. The gas supply pipe100 may be either fixed or not to the second housing 121. According tosuch a configuration, the sample may be placed beyond the edge of theapparatus. Thus, observation of a sample with a larger size than that ofEmbodiment 2 in which the covering member 122 is provided is possible.

Embodiment 4

This embodiment will describe a variation in which the positionalrelationship between the second housing 121 and the covering member 122is changed from the apparatus configuration of FIG. 2. FIG. 10 shows theoverall configuration of the charged particle microscope in thisembodiment. As in Embodiment 3, FIG. 10 shows only a primary part of theapparatus. In this configuration, a vacuum sealing member 128 forvacuum-sealing the first space 11 and the second space 12 is necessary.In this configuration, the mating portion 132 of the second housing islocated inside the apparatus. Thus, the size of the whole apparatus canbe reduced than those of Embodiments 1-3.

Example 5

This embodiment will describe a variation in which the second housing121 is vacuum-sealed on the upper side of the first housing in theapparatus configuration of FIG. 2. FIG. 11 shows the overallconfiguration of the charged particle microscope in this embodiment. Asin Embodiment 4, FIG. 11 shows only a primary part of the apparatus. Inthis configuration, using a pot-shaped attachment (i.e., the secondhousing 121), the attachment is embedded from above the first housing 7,and further, an electron optical column 2 is embedded from above theattachment. The second housing 121 is vacuum-sealed to the electronoptical column 2 by the vacuum sealing member 123, and further, thesecond housing 121 is vacuum-sealed to the first housing 7 by a vacuumsealing member 129. Such a configuration can increase the volume of thesecond space 12 from that in FIG. 2, and thus allows for the arrangementof a larger sample than that in Embodiment 2.

REFERENCE SIGNS LIST

-   0 Electron source (charged particle source)-   1 Optical lens-   2 Electron optical (charged particle optical) column-   3 Detector-   4 Vacuum pump-   5 Sample stage-   6 Sample-   7 First housing-   10 Thin film-   11 First space-   12 Second space-   14 Leak valve-   16 Vacuum pipe-   18 Column-   19 Plate-member support member-   20 Bottom plate-   35 Personal computer-   36 Upper-level controller-   37 Lower-level controller-   43,44 Communication line-   47 Thin film holding member-   50 Operation window-   51 Image display portion-   52 Image observation start button-   53 Image observation stop button-   54 Focus adjustment button-   55 Brightness adjustment button-   56 Contrast adjustment button-   57,59 Vacuum-evacuation button-   58,60 Air leak button-   100 Gas supply pipe-   101 Gas control valve-   102 Connecting portion-   103 Gas cylinder-   104 Pressure control valve-   105 Restriction member-   106 Camera-   107 Support plate-   108,109 Operation knob-   112 Gas emission start button-   113 Gas emission stop button-   114 SEM image display button-   115 Camera button-   116 SEM/Camera display button-   117 Gas emission time setting screen-   118 Child window-   119 Gas emission execution check box-   120 OK button-   121 Second housing-   122,130 Covering member-   123,124,125,126,128,129 Vacuum sealing member-   131 Main body portion-   132 Mating portion

The invention claimed is:
 1. A charged particle beam apparatuscomprising: a charged particle optical column that scans a sample with aprimary charged particle beam; a detector that detects reflectedelectrons or secondary electrons obtained by the scanning; a vacuumpump; a first housing in which the charged particle optical column issupported with respect to an apparatus installation plane; and a secondhousing comprising a main body portion that is inserted into the firsthousing, and a mating portion that is fixed to an outer wall face of thefirst housing, with a vacuum sealing member interposed therebetween,wherein the second housing is capable of maintaining a differentialpressure between a vacuum and atmospheric pressure in and out of thesecond housing, and the second housing has a structure that allows theprimary charged particle beam to penetrate or pass therethrough.
 2. Thecharged particle beam apparatus according to claim 1, wherein the sampleis stored in the first housing, an interior of the second housing isevacuated to a vacuum by the vacuum pump, and a pressure in the firsthousing can be maintained higher than a pressure in the second housing.3. The charged particle beam apparatus according to claim 2, wherein thefirst housing has an open face that allows the sample stored in aninterior of the first housing to be replaced while the interior of thesecond housing is maintained in a vacuum state.
 4. The charged particlebeam apparatus according to claim 3, wherein the second housing isattached to an outer wall of an upper surface of the first housing. 5.The charged particle beam apparatus according to claim 4, wherein thesecond housing comprises a thin film that allows the primary chargedparticle beam to penetrate therethrough.
 6. The charged particle beamapparatus according to claim 5, wherein the thin film is removably fixedto the second housing with a thin film holding member for holding thethin film interposed therebetween, and interiors of the first housingand the second housing can be evacuated to a vacuum by removing the thinfilm holding member from the second housing.
 7. The charged particlebeam apparatus according to claim 6, wherein the thin film holdingmember has a restriction member that restricts a distance between thesample and the thin film to prevent the sample from being located tooclose to the thin film.
 8. The charged particle beam apparatus accordingto claim 5, further comprising an observation device configured toobserve a gap between the thin film and the sample.
 9. The chargedparticle beam apparatus according to claim 5, further comprising a gasintroducing portion that introduces a replacement gas for replacing anatmosphere in the first housing.
 10. The charged particle beam apparatusaccording to claim 9, wherein the replacement gas is a light-element gasincluding a helium gas.
 11. The charged particle beam apparatusaccording to claim 5, further comprising a pressure control valve forcontrolling a pressure in the first housing, wherein, when the pressurein the first housing becomes higher than a predetermined value, thepressure control valve opens to reduce the pressure in the firsthousing.
 12. The charged particle beam apparatus according to claim 5,wherein the first housing is cuboid in shape, at least one part of oneside face of which is open, and the charged particle beam apparatusfurther comprises a covering member that covers the open face of thecuboid.
 13. The charged particle beam apparatus according to claim 12,further comprising a gas introducing portion that introduces areplacement gas for replacing an atmosphere in the first housing; and apressure control valve for controlling a pressure in the first housing,wherein the gas introducing portion and the pressure control valve areattached to the covering member, and a position of attachment of the gasintroducing portion to the covering member is higher than a position ofattachment of the pressure control valve to the covering member.
 14. Thecharged particle beam apparatus according to claim 12, furthercomprising a gas introducing portion that introduces a replacement gasfor replacing an atmosphere in the first housing, wherein the coveringmember has an opening part, the gas introducing portion is attached tothe covering member, and a position of attachment of the gas introducingportion to the covering member is higher than a position of the openingpart at the covering member.
 15. The charged particle beam apparatusaccording to claim 12, further comprising a sample stage that is fixedto the covering member and that moves the sample in a plane direction ora height direction.
 16. The charged particle beam apparatus according toclaim 5, further comprising a detector for detecting one or more ofions, electrons, photons, or X-rays that are emitted as a result ofscanning of the sample with the charged particle beam, the detectorbeing arranged in the first housing or the second housing, or a detectorthat detects transmission electrons obtained as a result of irradiationof the sample with the charged particle beam, the detector beingarranged in the first housing or the second housing.
 17. The chargedparticle beam apparatus according to claim 1, wherein the sample isstored in the second housing, an interior of a space enclosed by thefirst housing and the second housing is evacuated to a vacuum by thevacuum pump, and a pressure in a space in which the sample is stored canbe maintained higher than a pressure in the space enclosed by the firsthousing and the second housing.
 18. The charged particle beam apparatusaccording to claim 17, wherein the second housing has an open face thatallows the sample stored in an interior of the second housing to bereplaced while the interior of the first housing is maintained in avacuum state.
 19. The charged particle beam apparatus according to claim18, wherein the second housing is attached to an outer wall of a sideface of the first housing.
 20. The charged particle beam apparatusaccording to claim 19, wherein the second housing comprises a thin filmthat allows the primary charged particle beam to penetrate therethrough.